--- a/dom/media/webrtc/MediaEngineDefault.cpp
+++ b/dom/media/webrtc/MediaEngineDefault.cpp
@@ -410,17 +410,17 @@ MediaEngineDefaultAudioSource::Start(Sou
 
   if (!mSineGenerator) {
     // generate sine wave (default 1KHz)
     mSineGenerator = new SineWaveGenerator(aStream->GraphRate(), mFreq);
   }
 
   // AddTrack will take ownership of segment
   AudioSegment* segment = new AudioSegment();
-  aStream->AddAudioTrack(aID, mRate, 0, segment, SourceMediaStream::ADDTRACK_QUEUED);
+  aStream->AddAudioTrack(aID, aStream->GraphRate(), 0, segment, SourceMediaStream::ADDTRACK_QUEUED);
 
   // Remember TrackID so we can finish later
   mTrackID = aID;
 
   mLastNotify = 0;
   mState = kStarted;
   return NS_OK;
 }
@@ -466,17 +466,17 @@ MediaEngineDefaultAudioSource::NotifyPul
                                           SourceMediaStream *aSource,
                                           TrackID aID,
                                           StreamTime aDesiredTime,
                                           const PrincipalHandle& aPrincipalHandle)
 {
   MOZ_ASSERT(aID == mTrackID);
   AudioSegment segment;
   // avoid accumulating rounding errors
-  TrackTicks desired = aSource->TimeToTicksRoundUp(mRate, aDesiredTime);
+  TrackTicks desired = aSource->TimeToTicksRoundUp(aGraph->GraphRate(), aDesiredTime);
   TrackTicks delta = desired - mLastNotify;
   mLastNotify += delta;
   AppendToSegment(segment, delta, aPrincipalHandle);
   aSource->AppendToTrack(mTrackID, &segment);
 }
 
 void
 MediaEngineDefault::EnumerateVideoDevices(dom::MediaSourceEnum aMediaSource,

--- a/dom/media/webrtc/MediaEngineDefault.h
+++ b/dom/media/webrtc/MediaEngineDefault.h
@@ -183,17 +183,16 @@ public:
   NS_DECL_THREADSAFE_ISUPPORTS
 
 protected:
   ~MediaEngineDefaultAudioSource();
 
   TrackID mTrackID;
 
   TrackTicks mLastNotify; // Accessed in ::Start(), then on NotifyPull (from MSG thread)
-  TrackRate mRate; // ditto
   uint32_t mFreq; // ditto
 
   // Created on Start, then accessed from NotifyPull (MSG thread)
   nsAutoPtr<SineWaveGenerator> mSineGenerator;
 };
 
 
 class MediaEngineDefault : public MediaEngine